🌟 Human Heart & Circulation Cheat Sheet | Chambers, Valves, Cardiac Cycle Simplified 🌟

Chambers and Valves of the Heart

Human heart has four chambers:

Two upper thin-walled atria – receive blood from body/lungs.
Two lower thick-walled ventricles – pump blood to lungs/body.

🌟 Human Heart & Circulation Cheat Sheet | Chambers, Valves, Cardiac Cycle Simplified 🌟

Septa:

Atrioventricular septum – separates atria from ventricles.
Interatrial septum – separates left and right atria.
Interventricular septum – separates left and right ventricles; much thicker than interatrial septum.

Atrioventricular valves (between atria and ventricles):

Tricuspid valve – right atrium → right ventricle (3 cusps).
Bicuspid/Mitral valve – left atrium → left ventricle (2 cusps).
Function: Prevent backflow into atria during ventricular contraction.

Semilunar valves (at exit of ventricles):

Pulmonary valve – right ventricle → pulmonary artery.
Aortic valve – left ventricle → aorta.
Function: Prevent backflow from arteries into ventricles during relaxation.

Circulation of Blood through Heart

Heart acts as a double pump:

Pulmonary circulation – blood to lungs.
Systemic circulation – blood to all body organs (except lungs).

Right atrium receives deoxygenated blood via:

Superior vena cava
Inferior vena cava

Blood → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → pulmonary arteries → lungs.
Oxygenated blood from lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → aorta → body.
Left ventricle wall is about 3x thicker than right ventricle → needs more force to pump blood to entire body.

Cardiac Cycle (Heartbeat)

Heart works in continuous cycles:

Chambers relax → filled with blood (diastole).
Chambers contract → pump blood (systole).

Diastole:

Duration: ~0.4 s
Both atria & ventricles relaxed → filling with blood.

Atrial systole:

Duration: ~0.1 s
Atria contract → push blood into relaxed ventricles.

Ventricular systole:

Duration: ~0.3 s
Ventricles contract → blood pumped to pulmonary artery & aorta.
Tricuspid & bicuspid valves close; pulmonary & aortic valves open.

Total one heartbeat: ~0.8 s
In a lifetime, heart beats ~2.5 billion times.

Sounds of Heartbeat

“Lubb” – closing of tricuspid & bicuspid valves during ventricular contraction.
“Dubb” – closing of pulmonary & aortic valves during ventricular relaxation.
Can be heard with a stethoscope.

Heart murmurs:
Caused by valves not closing fully or opening narrowly → turbulent blood flow → hiss sound.
Serious cases can be treated by valve replacement (artificial or donor).

Human Heart – MCQs with Answers

How many chambers does the human heart have?
- A) 2
- B) 3
- C) 4 ✅
- D) 5
Which chambers of the heart are thin-walled?
- A) Ventricles
- B) Atria ✅
- C) Both
- D) None
Which septum separates the left and right atria?
- A) Interventricular septum
- B) Atrioventricular septum
- C) Interatrial septum ✅
- D) Pericardial septum
Which septum is thicker?
- A) Interatrial
- B) Interventricular ✅
- C) Atrioventricular
- D) None
What is the valve between right atrium and right ventricle called?
- A) Bicuspid
- B) Tricuspid ✅
- C) Pulmonary
- D) Aortic
The bicuspid valve is also known as:
- A) Tricuspid
- B) Mitral ✅
- C) Pulmonary
- D) Aortic
Which valves open when ventricles contract?
- A) Tricuspid and Bicuspid
- B) Pulmonary and Aortic ✅
- C) All valves
- D) None
Which valves close during ventricular systole?
- A) Pulmonary and Aortic
- B) Tricuspid and Bicuspid ✅
- C) All valves
- D) None
The right atrium receives blood via:
- A) Pulmonary veins
- B) Superior and inferior vena cava ✅
- C) Aorta
- D) Pulmonary artery
Deoxygenated blood leaves the right ventricle through which vessel?
- A) Pulmonary trunk ✅
- B) Aorta
- C) Pulmonary veins
- D) Superior vena cava
Oxygenated blood returns to the heart via:
- A) Pulmonary arteries
- B) Pulmonary veins ✅
- C) Aorta
- D) Inferior vena cava
Left ventricle wall is thicker than the right because:
- A) Pumps blood to lungs
- B) Pumps blood to whole body ✅
- C) It has more valves
- D) None of the above
What is the name of the phase when heart chambers are relaxed?
- A) Systole
- B) Diastole ✅
- C) Cardiac cycle
- D) Pulse
During which phase do atria contract?
- A) Atrial diastole
- B) Atrial systole ✅
- C) Ventricular systole
- D) Ventricular diastole
Ventricles contract during:
- A) Atrial systole
- B) Ventricular systole ✅
- C) Diastole
- D) Cardiac pause
Duration of one heartbeat is approximately:
- A) 0.5 sec
- B) 0.8 sec ✅
- C) 1.0 sec
- D) 1.2 sec
“Lubb” sound of the heart is caused by:
- A) Closing of semilunar valves
- B) Closing of AV valves ✅
- C) Opening of AV valves
- D) Opening of semilunar valves
“Dubb” sound of the heart is caused by:
- A) Closing of semilunar valves ✅
- B) Closing of AV valves
- C) Opening of AV valves
- D) Opening of semilunar valves
Blood from the left ventricle is pumped into:
- A) Pulmonary artery
- B) Aorta ✅
- C) Superior vena cava
- D) Pulmonary vein
Blood from the right ventricle is pumped into:
- A) Pulmonary artery ✅
- B) Aorta
- C) Superior vena cava
- D) Pulmonary vein
Heart murmur is caused by:
- A) Complete valve closure
- B) Valve defects causing turbulent blood flow ✅
- C) Healthy blood flow
- D) Thick myocardium
Which ventricle has a thicker wall?
- A) Right
- B) Left ✅
- C) Both equal
- D) None
Pulmonary circulation carries blood to:
- A) Lungs ✅
- B) Body
- C) Brain only
- D) Heart
Systemic circulation carries blood to:
- A) Lungs
- B) Whole body except lungs ✅
- C) Heart only
- D) None
The lifetime heartbeats of an average person are approximately:

A) 1 billion
B) 2.5 billion ✅
C) 5 billion
D) 10 billion

Human Heart – Exam-Based Short Q&A

Q: How many chambers are present in the human heart?
A: The human heart has 4 chambers: 2 atria (upper) and 2 ventricles (lower).
Q: Which chambers are thin-walled and why?
A: Atria are thin-walled because they only receive blood from veins and do not pump it with high pressure.
Q: Which septum separates the atria?
A: Interatrial septum separates the left and right atria.
Q: Which septum separates the ventricles and why is it thicker?
A: Interventricular septum separates the left and right ventricles; it is thicker because the left ventricle pumps blood to the whole body.
Q: Name the valve between right atrium and right ventricle.
A: Tricuspid valve; it prevents backflow of blood into the right atrium during ventricular contraction.
Q: What is the bicuspid valve and its function?
A: Also called mitral valve, it is between left atrium and left ventricle, preventing backflow of oxygenated blood into the atrium.
Q: When do the semilunar valves open?
A: Pulmonary and aortic valves open during ventricular systole to allow blood to flow into arteries.
Q: When do the atrioventricular valves close?
A: Tricuspid and bicuspid valves close during ventricular contraction to prevent backflow into atria.
Q: How does deoxygenated blood enter the right atrium?
A: Through superior and inferior vena cava from the body.
Q: Where does the right ventricle pump blood?
A: Into the pulmonary trunk, which carries blood to the lungs for oxygenation.
Q: How does oxygenated blood return to the heart?
A: Pulmonary veins carry oxygen-rich blood from the lungs to the left atrium.
Q: Why is the left ventricle wall thicker than the right?
A: Because it must generate higher pressure to pump blood throughout the entire body.
Q: What is diastole?
A: Diastole is the relaxation phase when chambers fill with blood.
Q: What is atrial systole?
A: Contraction of atria to push blood into the ventricles.
Q: What is ventricular systole?
A: Contraction of ventricles to pump blood into the pulmonary artery and aorta.
Q: Approximate duration of one complete heartbeat?
A: About 0.8 seconds: diastole 0.4 s, atrial systole 0.1 s, ventricular systole 0.3 s.
Q: Which valves cause the “Lubb” heart sound?
A: Closing of tricuspid and bicuspid (AV) valves during ventricular contraction.
Q: Which valves cause the “Dubb” heart sound?
A: Closing of pulmonary and aortic (semilunar) valves during ventricular relaxation.
Q: Where does blood from left ventricle go?
A: Into the aorta to supply oxygenated blood to the entire body.
Q: Where does blood from right ventricle go?
A: Into the pulmonary artery to reach the lungs.
Q: What is a heart murmur and its cause?
A: A heart murmur is an abnormal hiss caused by incomplete or narrow valve closure, creating turbulent blood flow.
Q: What is the main difference between left and right ventricles?
A: Left ventricle has a thicker wall and pumps blood to whole body; right ventricle pumps blood to lungs.
Q: What is pulmonary circulation?
A: It carries deoxygenated blood from right ventricle to lungs and returns oxygenated blood to left atrium.
Q: What is systemic circulation?
A: It carries oxygenated blood from left ventricle to all body parts except lungs, and returns deoxygenated blood to right atrium.
Q: Approximate number of heartbeats in an average human lifetime?
A: Around 2.5 billion beats.

Human Heart – Long Questions (Exam-Oriented)

Describe the structure of the human heart including its chambers, wall, and pericardium.
Explain the differences between atria and ventricles in terms of structure and function.
Draw a labeled diagram of the human heart and explain the function of each part.
Explain the structure and function of the atrioventricular valves.
Explain the structure and function of the semilunar valves.
Describe the circulation of blood through the heart including pulmonary and systemic circulation.
Explain why the wall of the left ventricle is thicker than that of the right ventricle.
Define cardiac cycle and describe its phases including diastole, atrial systole, and ventricular systole with duration.
Explain the sounds of the heartbeat and how they are produced.
What are heart murmurs? Describe their causes and possible remedies.
Describe the differences between pulmonary circulation and systemic circulation.
Explain how the heart functions as a double pump to maintain oxygenated and deoxygenated blood separation.
Describe the role of superior and inferior vena cava, pulmonary artery, pulmonary veins, and aorta in blood circulation.
Discuss the mechanism that prevents backflow of blood in the heart.
Explain the importance of the cardiac cycle in maintaining continuous blood circulation.
How does the structure of the heart relate to its function in pumping blood efficiently throughout the body?
Explain how the human heart adapts to the demands of exercise and increased oxygen requirement.
Describe the conduction system of the heart (SA node, AV node, bundle of His, Purkinje fibers) and its role in maintaining heart rhythm.
Explain the difference between atrial and ventricular systole in terms of pressure changes and valve movements.
Describe the clinical significance of heart sounds and murmurs in diagnosing heart diseases.